Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-In HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Based on their external and internal structures, secondary batteries may be generally classified into a cylindrical battery, a prismatic battery, and a pouch-shaped battery. Especially, the prismatic battery and the pouch-shaped battery, which can be stacked with high integration and have a small width to length ratio, have attracted considerable attention.
An electrode assembly having a cathode/separator/anode structure, which constitutes a secondary battery, may be generally classified as a jelly-roll (winding) type electrode assembly or a stack type electrode assembly, based on the structure of the electrode assembly. The jelly-roll type electrode assembly is manufactured by coating a metal foil to be used as a current collector with an electrode active material, drying and pressing the coated metal foil, cutting the dried and pressed metal foil into the form of a band having a predetermined width and length, isolating an anode and a cathode from each other using a separator, and helically winding the anode/separator/cathode structure. The jelly-roll type electrode assembly is suitable for a cylindrical battery; however, the jelly-roll type electrode assembly is not suitable for a prismatic battery or a pouch-shaped battery because stress locally concentrates on the battery with the result that the electrode active material is detached, or the battery may be deformed due to repetitive contraction and expansion of the battery caused during charge and discharge of the battery
On the other hand, the stack type electrode assembly is configured to have a structure in which a plurality of unit cathodes and a plurality of unit anodes are sequentially stacked. The stack type electrode assembly has an advantage in that the stack type electrode assembly can be configured to have a prismatic structure; however, the stack type electrode assembly has disadvantages in that a process for manufacturing the stack type electrode assembly is complicated, and, when external impact is applied to the stack type electrode assembly, electrodes of the stack type electrode assembly are pushed with the result that a short circuit may occur in the stack type electrode assembly.
In order to solve the above-described problems, there has been developed an improved electrode assembly which is a combination of the jelly-roll type electrode assembly and the stack type electrode assembly, i.e. a stack/folding type electrode assembly configured to have a structure in which full cells having a cathode/separator/anode structure of a predetermined unit size or bicells having a cathode (anode)/separator/anode (cathode)/separator/cathode (anode) structure of a predetermined unit size are folded using a long continuous separator sheet. Examples of such a stack/folding type electrode assembly are disclosed in Korean Patent Application Publication No. 2001-82058, No. 2001-82059, and No. 2001-82060, which have been filed in the name of the applicant of the present patent application.
In the stack/folding type electrode assembly, however, the unit cells are arranged on the long continuous separator sheet, and the unit cells and the separator sheet are folded while the unit cells and the separator sheet are held at opposite ends thereof. Consequently, a space and a system necessary to carry out such manufacturing processes are essentially required, and therefore, a manufacturing method is very complicated, and equipment investment costs are high.
Therefore, there is a high necessity for a battery cell manufacturing device that is capable of improving manufacturing processability while minimizing manufacturing costs and improving capacity and quality of a battery as compared with another battery of the same standard.